Graphene and other 2D materials are formed with large two dimensional crystalline structures, and they are generally highly useful materials, but they are difficult and expensive to manufacture. A machine and method for making such materials is disclosed herein that significantly reduces the cost of 2D materials, and the technique is scalable, meaning it can be made larger and faster with relative ease.
In one embodiment, an apparatus for producing a 2D material, such as graphene, includes a forming sheet suitable for growing (forming) the 2D material, and the forming sheet is disposed on the surface of a carrier substrate. A furnace is provided in a configuration to form a confining space around the carrier substrate and the forming sheet, and the confining space is open to atmosphere around the furnace such that gas may flow out of the confining space to atmosphere. The furnace also includes a support configured to support the carrier substrate in the furnace, and within the furnace, a first furnace surface is disposed immediately adjacent to and spaced apart from the forming sheet when the carrier substrate is disposed on the support. In this configuration, a volume is formed between the first furnace surface and the forming sheet, and such volume facilitates gas flow within the furnace to effectively and efficiently deposit large crystalline structures of 2D material onto the forming sheet. At least one supply port provides a flow of gas into the volume, and a gas supply provides a flow of purge gas through the supply port to purge the volume and also supplies a flow of donor gas through the supply port and into the volume. A heater within the furnace heats the forming sheet to a temperature sufficient to form 2D material, such as graphene, on the forming sheet when a donor gas is supplied into the volume.
The purge gas is chosen to remove elements, molecules or compounds that would interfere with the production of the 2D material. For example, oxygen would typically interfere with the production of 2D material, such as graphene, and oxygen may be purged with a gas such as argon or nitrogen. The donor gas is chosen to supply the material needed to form the 2D material. For example, to form graphene the donor gas should supply carbon atoms and one appropriate donor gas would be methane. To make another 2D material with this apparatus and method the donor gas is changed to donate the desired element or molecule and the operating parameters (temperature and forming sheet material) are adjusted for the desired 2D material.
In the production of 2D material, the furnace may be constructed in whole or part of quartz. The quartz plate may be used to form the first furnace surface, and multiple ports are formed in the quartz plate extending through the first furnace surface for delivering gases to the confining space in the furnace between the first furnace surface and the forming sheet. Multiple ports are connected to a plurality of passageways formed in the quartz plate, and the passageways are connected to a gas supply. Purge gases and donor gases are transmitted through the passageways to the plurality of ports for first purging the volume inside the furnace and then providing the donor gas to form 2D material on the forming sheet within the furnace. The heater may be disposed adjacent to the quartz plate on the opposite side of the quartz plate from the first furnace surface such that the heater and the forming sheet are positioned on opposite sides of the quartz plate and heat from the heater is transmitted through the quartz plate to the forming sheet.
The first furnace surface and the forming sheet are configured so that the volume between them has a rectangular cross-section, with the width of the cross-section being larger than the height of the cross-section. The width is at least 3 times the height but the width is less than 1,000,000 times the height. Preferably, the width is less than 1000 times the height. The configuration of the volume combined with the configuration of the ports and the flow rates of the gases is designed to produce a substantially nonturbulent, laminar flow of the donor gases across the forming sheet. The purge gases will also have the nonturbulent laminar flow across the forming sheet which will increase the efficiency with which the purging process takes place.
In one embodiment, multiple ports are formed in the first furnace surface and are disposed in a pattern extending across the first furnace surface. Thus, the ports are disposed adjacent to the forming sheet in a pattern that extends across the forming sheet from one side to an opposite side forming sheet. This configuration will cause a desired even distribution of the gases across the forming sheet. A plurality of patterns may be used. For example, one pattern may be a line of ports extending across the first furnace surface and the second pattern may be V-shaped with a point of the V disposed in the mid-region of the surface and two sides of the V extending across the surface.
In accordance with a more particular embodiment, the furnace may be configured to form a confining space around the carrier substrate and the forming sheet, and the confining space may be open to the atmosphere around the furnace. In this configuration, gas may flow out of the furnace, but the confining space will restrict the flow of gas out of the furnace so that the confining space is continuously filled with the desired gas. Also, an entrance may be formed in the furnace, penetrating the confining space of the furnace and dimensioned to receive the carrier substrate and forming sheet. The entrance may allow gases to flow out of the furnace, but it will be part of the confining space and will restrict the flow of gases out of the confining space such that a desired gas is maintained within the confining space. A transport mechanism is provided for moving the carrier substrate and the forming sheet into the entrance of the furnace and within the furnace along a direction of travel. An exit, similar to the entrance, is also formed in the furnace penetrating the confining space so that the transport mechanism may move the carrier substrate and the forming sheet along the direction of travel and out of the furnace through the exit.
A gas chamber may be formed around the confining space of the surface for capturing and containing the purge gases and the donor gases that flow out of the furnace. Thus, a gas atmosphere is formed within the gas chamber around the furnace that is substantially free of undesirable gases, such as oxygen. Thus, the gas chamber will protect the furnace from infiltration of undesirable gases from outside the furnace. The gas chamber is preferably formed by a hood system that contains the entire furnace, and gases within the hood system may be controlled by a variety of mechanisms. For example, gases may be released from the hood system at a controlled rate that is substantially equal to the rate at which gases are introduced into the furnace. Thus, the hood system may remain slightly pressurized with respect to the outside atmosphere so that gases flow out of the furnace into the gas chamber, and out of the gas chamber into the surrounding environment or atmosphere.
The furnace may also be provided with a plurality of carrier substrates and the forming sheet may be one or more forming sheets suitable for growing graphene with at least one forming sheet disposed on each of the plurality of carrier substrates. So, the number of forming sheets may be equal to the number of carrier substrates or may be greater than the number of carrier substrates. Multiple forming sheets may be carried on each carrier substrate. Alternatively, a single forming sheet could be carried by multiple carrier substrates. In such case, at least one forming sheet would still be disposed on each of the plurality of carrier substrates. The transport mechanism is configured to move the plurality of carrier substrates into the entrance of the furnace, through the furnace along a travel path and out the exit of the furnace, so that graphene is grown on each forming sheet as it is heated and passed through the donor gases in the furnace.
The method of making graphene as described above may be described as introducing a purge gas into a space within a furnace to purge the space of undesirable gases such as oxygen and introducing a donor gas into the space. A forming sheet suitable for forming graphene is moved within the space when the donor gases are within the space, and the forming sheet is heated within the space to a temperature sufficient to form 2D material. Thus, 2D material is formed on the moving forming sheet within the furnace.
In accordance with a more particular method of making 2D material, multiple carrier substrates are used and new carrier substrates are continuously moved into the furnace to form a train of carrier substrates that moves into and through the furnace. At least one forming sheet is disposed on each carrier substrate and each forming sheet is heated as it moves through the furnace to a temperature sufficient to form 2D material on the forming sheet. After the forming sheet is heated, each forming sheet is exposed to a donor gas to form 2D material on the forming sheet. Then, each carrier and forming sheet is moved out of the furnace through the exit.
In accordance with another aspect of the method, purge gases are introduced into a confining space within the furnace and into a gas chamber surrounding the furnace. Thus, purge gases continuously flow into and out of the confining space and the gas chamber until the gas chamber and space are substantially oxygen free. Then, donor gases are introduced into the confining space and the donor gases flow out of the furnace into the gas chamber. At least some of the purge gas and the donor gas that escapes from the confining space within the furnace is captured and retained in the gas chamber to maintain an environment in the gas chamber around the furnace that is substantially free of undesirable gases such as oxygen.